The Colossal Squid Has a Doughnut Shaped Brain With Their Esophagus Running Through the Hole

Today I found out the Colossal Squid, which is the largest known squid in terms of mass on Earth, has a doughnut shaped brain with their esophagus running through the hole in the center.

This hole through their brain isn’t very large at all with their esophagus diameter at just around 10 mm (.39 inches). Their brain itself isn’t that big either, weighing in at just about 100 grams (.22 pounds).

This somewhat unique feature of the colossal squid, also known as the “Giant Cranch Squid” and technically as “Mesonychoteuthis hamiltoni”, has a side effect that the squid has to tear up its food into very small pieces in order not to injure their tiny brains as they swallow.

This isn’t much of a problem as despite the colossal squid’s large size of about 39-46 ft. long (11.8-14 meters) and weighing 1000-1500 pounds (453-690 kg), they don’t actually eat very much at all, which is a very recent discovery. Due to the extreme cold temperatures the squids live in (as far down as 7200 ft deep or 2.2 km, with their habitat from the Southern tip of Africa down throughout the Antarctic), they have very slow metabolisms. So slow, in fact, that they can live comfortably on just 30 grams (.07 pounds) of food per day. As such, it is now thought that rather than being aggressive hunters, the colossal squid probably takes more of a “sit and wait” approach for acquiring food.

Once some sea creature swims or floats along within the colossal squid’s reach, the squid simply reaches out and grabs it with its suckered tentacles that are also equipped with sharp hooks. They then bring the thing in towards their large and powerful beak and tear small bits of flesh at a time that can easily pass through the hole in their brain. Probably not the most pleasant death to go through, particularly as the squid is known to chow down on fairly large prey at times, such as the Patagonian toothfish which can be as big as 2.3 m. or 7+ ft. long. Thanks to this ultra-slow metabolism, a single toothfish, at least as far as mass, is all the squid needs to catch to survive for about 2/3 of a year.

Of course, colossal squid, while big, are not just predators, but also prey. Among other animals, Sperm whales are known to like to feed on them, with their beaks often being found in whale stomachs. In fact, about 14% of the squid beaks found in the stomachs of Antarctic sperm whales are from the colossal squid, with an estimated 77% of the biomass eaten by these whales being from these monsters of the sea. The downside for these whales is that the colossal squid has those very sharp hooks on their tentacles, so getting their flesh tore up a bit seems to be a common occurrence after trying to eat one, at least judging from the number of scars found on the sperm whales thought to be from the colossal squid.

If you liked this article and the Bonus Facts below, you might also like:

The colossal squid has the largest eyes of any known animal, with even a partially collapsed eye of a dead colossal squid measuring 11 inches (27 cm) wide and 4.7 inches (12 cm) across. It is thought that a non-partially collapsed eye of the squid would probably be more like 12-16 inches (30-40 cm) across. For reference, their pupils are large enough to take in about 144 times as much light as a typical human eye, which is helpful when one lives so deep in the ocean. It’s also estimated that about 80% of their tiny brains are specialized to handle visual information.

Another interesting feature of the colossal squid are statoliths. The squid has two of these within their brain. These are tiny bone-like objects sitting in a small chamber. Using the orientation of the little bone, these structures allow the squid to sense which way is up and which way is down while they float around in the pitch black depths of the ocean.

Colossal squid have blue blood, rather than red as in humans. Their blood is given this color thanks to haemocyanin.

It is thought that colossal squid probably emit bio-luminescent ink, rather than dark ink as many squid do. Obviously dark ink would be useless to the squid in the environment they live in.

The largest colossal squid ever caught was captured in 2007, weighing about 1100 lb and was an estimated 10 m long (33 ft), though it shrunk to about half that size post-mortem. It’s thought they can get much bigger, though, because the beak size of this squid was significantly smaller than the largest known beaks of the colossal squid found in the stomachs of whales.

This largest specimen caught was not what the fisherman were fishing for. They had been fishing for Patagonian toothfish, but when they brought the line up, the colossal squid was attached. They attempted to remove the squid from the line, but despite their efforts, the squid would not release its prey. So they went ahead and reeled it in too and froze it for transport.

The first part of the colossal squid’s scientific name, “Mesonychoteuthis hamiltoni”, comes from the Greek “mesos”, meaning “middle”; then “nychus”, meaning “claw”; and “teuthis”, meaning “squid”.

It is thought that the female colossal squids are larger than the males.

Other animals known to feed on the colossal squid include pilot whales, elephant seals, sleeper sharks, and albatrosses.

The colossal squid has 3 hearts, one main heart and then two much smaller hearts near each gill.